1. Field of the Invention
This invention is directed to a fitting that provides a granular material inlet and an air and dust outlet for a granular material storage vessel such is a vessel into which plastic pellets or plastic regrind material is loaded before that material is utilized in an injection molding machine. The fitting provides a material outlet and an air and dust outlet in close proximity to each other whereby the material is conveyed into the vessel while the air stream which conveyed the material is directed through the fitting to a filter or other appropriate mechanism.
2. Description of the Prior Art
Conventionally, granular material is conveyed to material storage vessels through tubes that cause the granular material to enter the storage vessel at one port and then cause the air stream which conveyed the granular material to leave the vessel at a different port in the vessel so that the air stream travels through the vessel. The air stream carrying the granular material to the vessel is created either by forcing compressed air through the system or by drawing a vacuum at some point beyond the vessel and drawing material in an air stream created by that vacuum into the vessel.
In a vacuum conveying system, the granular material is usually conveyed into the vessel through an inlet tube located horizontally in the vessel wall. Conveying air and small particles of dust pass through a filter or screen located above the inlet in the vessel and positioned between the vessel itself and the lid of the vessel. The granular material is retained within the vessel and an air outlet tube from the lid allows the air and dust to pass through vacuum lines to a dust collector and then to a vacuum source such as a vacuum pump. Often, a sequence valve to direct the flow of air and material is mounted within or on top of the lid or located remotely overhead on the main vacuum header line.
Serious disadvantages result in a vacuum conveying system from the present use of separate inlet and outlet ports within the vessel. A sequence valve mounted on the lid of the vessel adds extra height to the overall vessel assembly and adds weight to the lid which makes it more difficult to remove the lid. This extra weight makes it more difficult to remove the filter or screen for cleaning. If the sequence valve is located in the vacuum header line, it is usually 15 to 20 feet above the vessel. This distance makes it difficult to maintain the sequence valve and there is no visual determination of the operation of the sequence valve. With this type of vacuum conveying, the filter screen is usually 9" to 27" in diameter and difficult to clean. It is expensive to manufacture, it is easily damaged, and it is difficult to maintain a vacuum seal around the periphery of the screen.
When granular material is conveyed by pressure such as the use of compressed air, the entry tube to the vessel is usually straight in or is tangential to the cylindrical vessel that has a cone shaped bottom. Cartridge type filters are located at the top of the vessel to trap dust and any material that is carried over by the air. A disadvantage to the pressure conveying systems is that much of the material is carried by the air into the filter cartridge folds which makes the filter cartridge difficult to clean. In addition, most of the vessels with pressure conveying are designed as cyclone separators but they do not effectively operate as such. Accordingly, the effort to produce cyclone separation increases the height of the storage vessel.